Modern microprocessors require the output of high current at relatively low voltage levels, typically in the range of zero to five volts. Further, although microprocessor requires high current, the current demands for requirements fluctuate widely. For example, in the sleep or idle mode a microprocessor might require currents in the range of 0.5 A to 5 A while a microprocessor in a faster computing mode might require currents in the range of 10 A to 100 A. However even though current requirements fluctuate widely, microprocessor specifications require that the voltage limits remain relatively stable, no matter what the operational mode of the microprocessor.
Requirements for tight voltage regulation in response to highly variable current demands mean that the main power supply output can no longer be fed directly to the microprocessor. Instead, a voltage regulator is used to deliver a tightly controlled voltage to the microprocessor. A local voltage regulator supplies a high level of DC current and minimizes the uncertainty in voltage drops between the main power supply and the microprocessor.
Although a voltage regulator circuit provides tight voltage regulation, it must be placed in close proximity to the microprocessor. If the voltage regulator is too far from the microprocessor, impedance between the voltage regulator and microprocessor increases, causing poor voltage regulation at the microprocessor. Further, an increase in impedance decreases speed and increases voltage drops. As the clock speed requirements for microprocessors increase, increases in impedance become less and less acceptable.
A problem with positioning the voltage regulator circuit in close proximity to the microprocessor is that other peripheral devices that work with the microprocessor may be displaced. For example, memory chips, etc. also need to be in close proximity to microprocessor. Thus, the voltage regulator circuit uses up a significant amount of board space which could otherwise be used effectively for the placement of cache memory or other integrated circuits peripheral to the microprocessor, which also need to be close to the microprocessor for reasons of signal integrity. Further, because space constraints are so tight, it is difficult to customize a board for the customer by adding different optional components since board space near the microprocessor is so limited.
A method and apparatus for locating a voltage regulator circuit close to microprocessor while minimizing the required board space and minimizing impedance is needed.